The present disclosure relates generally to semiconductor processing equipment and, more particularly, to a gas box for delivering contaminant-free, precisely metered quantities of process gases to semiconductor process chambers. Even more particularly, the present disclosure relates to a system and method for dividing flow from a single gas box among multiple process chambers.
The fabrication of semiconductor devices often requires the careful synchronization and precisely measured delivery of as many as a dozen gases to a process chamber. Various recipes are used in the fabrication process, and many discrete processing steps where a semiconductor device is cleaned, polished, oxidized, masked, etched, doped, metalized, etc., can be required. The steps used, their particular sequence and the materials involved all contribute to the making of particular devices.
Accordingly, wafer fabrication facilities are commonly organized to include areas in which chemical vapor deposition, plasma deposition, plasma etching, sputtering and other similar gas manufacturing processes are carried out. The processing tools, be they chemical vapor deposition reactors, vacuum sputtering machines, plasma etchers or plasma enhanced chemical vapor deposition, must be supplied with various process gases. Pure gases must be supplied to the tools in contaminant-free, precisely metered quantities.
In a typical wafer fabrication facility the gases are stored in tanks, which are connected via piping or conduit to a gas box. The gas box delivers contaminant-free, precisely metered quantities of pure inert or reactant gases from the tanks of the fabrication facility to a process tool. The gas box, or gas metering system includes a plurality of gas paths having gas metering units, such as valves, pressure regulators and transducers, mass flow controllers and filters/purifiers. Each gas path has its own inlet for connection to separate sources of gas, but all of the gas paths converge into a single outlet for connection to the process tool.
Sometimes dividing the combined process gases among multiple process chambers is desired. In such cases, the single outlet of the gas box is connected to multiple process chambers through secondary flow paths. To insure that the primary flow of the outlet of the gas box is divided equally among the secondary flow paths, flow restrictors are placed in each secondary flow path. Such a technique of dividing flow, however, requires that pressure upstream of the secondary flow paths be kept relatively high (e.g., 30 to 45 PSIA). Otherwise, the technique may not be as accurate when the upstream pressure needs to be kept lower (e.g., less than 15 PSIA) for safety or other reasons.
What is still desired, therefore, is a system and method for dividing a single flow of gas into two or more secondary flows of known, precise values, without requiring a high upstream pressure.
Accordingly, the present disclosure provides a system for dividing a single flow of gas into two or more secondary flows of known, precise values, without requiring a high upstream pressure. The system includes an inlet for receiving the single gas flow, and first and second flow lines connected to the inlet. A mass flow meter measures gas flow through the first line and provides a signal indicative of the measured flow rate. A restrictor restricts gas flow through the first line to a desired flow rate, and has a smallest cross-sectional flow area selected to provide an upstream pressure high enough to allow the mass flow meter to operate properly and lower than a predetermined upper pressure limit. The system also has a mass flow controller controlling gas flow through the second line. The mass flow controller receives the signal indicative of the measured flow rate from the mass flow meter and maintains a flow rate through the second line based on the signal.
According to one aspect of the present disclosure, the smallest cross-sectional flow area of the restrictor is selected such that the predetermined upper pressure limit is equal to about 15 PSIA. According to another aspect, the mass flow meter and the mass flow controller are provided with the same flow range.
According to another aspect of the present disclosure, the mass flow controller maintains a flow rate through the second line substantially equal to the measured flow rate of the first line. According to an additional aspect, the system also includes a controller for proportionally adjusting the signal indicative of the measured flow rate from the mass flow meter prior to the signal being received by the mass flow controller, such that the mass flow controller maintains a flow rate through the second line substantially equal to a predetermined ratio of the measured flow rate of the first line.
According to an additional aspect, the system further includes at least a third flow line connected to the inlet, and a mass flow controller controlling gas flow through the third line. The mass flow controller of the third line receives the signal indicative of the measured flow rate from the mass flow meter and maintains a flow rate through the third line based on the signal. According to still another aspect, the system includes at least one controller for proportionally adjusting the signal indicative of the measured flow rate from the mass flow meter prior to the signal being received by the mass flow controllers, such that the mass flow controllers maintain flow rates through the second and the third lines substantially equal to a predetermined ratio of the measured flow rate of the first line.
These and other features and advantages of the present disclosure will become more apparent to those of ordinary skill in the art after reading the following detailed description of the preferred embodiments, which are illustrated in the attached drawing figures.